Colitis: Causes and Risk Factors

There are a variety of causes for inflammation in the colon

Table of Contents
View All
Table of Contents

Colitis is a broad term that refers to inflammation in the colon—which is the biggest part of the largest intestine. Colitis is not a disease in and of itself, but is rather a sign of a condition.

There are a variety of causes of colitis, including infection, inflammatory bowel disease (IBD), microscopic colitis, ischemic colitis, and allergic colitis (a condition found in infants).

A Black, female physician uses a tablet to explain something to an older patient.

aldomurillo / Getty Images

Common Causes

Inflammatory Bowel Disease 

The various forms of IBD, which include Crohn’s disease, ulcerative colitis, and indeterminate colitis, can all lead to the development of colitis. The causes of IBD are not understood, but theories do exist.

These diseases are called “idiopathic,” meaning that it’s not yet clear what the underlying series of changes in the body are that lead to the development of the disease. However, some clues are being investigated to learn more about causes.

There is a genetic component—the genes that are associated with IBD are passed down through families. More than 200 genes that have been identified as having a connection to IBD.

In addition, evidence is growing that another piece to developing an IBD is what’s called an “environmental trigger.” This is something external that interacts with the genes and the gut microbiome—the bacteria and other organisms that normally live in the gut and aid in digestion.

This sets off the inflammation in the colon or other parts of the digestive tract, as is the case in Crohn’s disease.

Clostridium difficile Colitis

Clostridium difficile (C. difficile) is a type of bacteria normally found in the colon as part of the healthy gut microbiome, but in small amounts. However, if the C difficile grows out of control, it can cause a type of colitis.

The symptoms of C. difficile colitis often include diarrhea, although some people can have an infection without any symptoms.

The risk factors for developing an infection with C. difficile include:

  • Frequent or recent hospitalization
  • Treatment with antibiotics (including clindamycin, cephalosporins, and fluoroquinolones) 
  • Treatment with proton pump inhibitors (PPIs) or histamine-2 receptor antagonists (H2RAs)
  • Weakened immune system, such as from age or treatment with chemotherapy
  • Having an underlying condition, such as chronic kidney disease, human immunodeficiency virus (HIV), solid organ or hematopoietic stem cell transplantation, or IBD

Microscopic Colitis

The cause of microscopic colitis is not understood. It’s a common condition, and the symptoms include chronic diarrhea. In some cases, inflammation may be found in the mucosa of the colon. Some of the risk factors being investigated include:

  • Abnormal bile acid absorption
  • Autoimmune conditions
  • Bacterial antigens
  • Genetic predisposition
  • Medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs), PPIs, and selective serotonin reuptake inhibitors
  • Smoking

Ischemic Colitis

The ultimate cause of ischemic colitis is a lack of blood flow to a section of the colon. Without an adequate blood supply, the tissue in the colon becomes injured or may begin to die.

There are many different reasons why an artery or blood vessel could become damaged or blocked. However, a specific cause is not found for most cases of ischemic colitis.

Ischemic colitis is not something that can be predicted; it’s not known who will develop the condition. However, some factors may put people more at risk of developing ischemic colitis. These include:

Allergic Colitis

Allergic colitis is found in breastfed infants. Blood in the stool is often the only symptom.

The cause is thought to be from a food allergy, possibly an allergic reaction to dairy. However, even when the breastfeeding parent eliminates dairy from the diet, the bleeding sometimes still persists. For that reason, it’s thought that there might be other causes, but they’re not yet understood.

An elimination diet in the breastfeeding parent or changing the baby over to specialized formula might help shorten the time of the bleeding. The bleeding may also stop on its own after several weeks.


The cause of colitis will depend on the type. There is no one genetic reason that makes a person more likely to develop colitis. However, some connections can be made between genetics and certain forms of colitis.

Some genes have been found to be associated with IBD. It’s thought that there may be many more varieties of IBD than are currently defined. The variations in the genes connected to these diseases may help explain why IBD is so individualized, with patients experiencing a wide range of symptoms and extra-intestinal manifestations.

There has also been some research that one type of microscopic colitis—collagenous colitis—might be connected to certain genes. However, how this might help in diagnosis and treatment isn’t yet known because so little is understood about the condition.

Lifestyle Risk Factors

In IBD, it is known that smoking cigarettes is associated with a greater risk of developing Crohn’s disease and worsening the condition. (The same connection isn’t made with ulcerative colitis.)

Smoking also tends to worsen the course of Crohn’s disease. People with IBD, and especially Crohn’s disease, are usually counseled by their healthcare team to quit smoking.

Some early research on diets and the development of IBD and its management have been conducted, but there are as yet no firm guidelines to be used for all patients.

For instance, one study found a connection between a diet high in “ultra-processed foods” and a diagnosis of IBD. As yet, the specifics haven’t been narrowed down to identify a particular food or food type that’s associated with a higher risk.


Colitis (inflammation of the colon) is seen in a variety of conditions. Some of the most common are C. difficile infection, inflammatory bowel disease (IBD), microscopic colitis, ischemic colitis, and allergic colitis. There may be a genetic risk factor for some of these conditions, and smoking is known to be a risk factor for Crohn’s disease.

A Word From Verywell

For the most part, causes of colitis aren’t known or may not be avoidable. Risk factors include age and having other conditions, and these are things that can’t be changed.

What is important is to get medical attention when there is blood in the stool or abdominal pain. In some cases, colitis can be chronic, but if it is acute, it may need treatment right away.

10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Guan Q. A comprehensive review and update on the pathogenesis of inflammatory bowel disease. J Immunol Res. 2019;2019:7247238. doi:10.1155/2019/7247238

  2. Depestel DD, Aronoff DM. Epidemiology of Clostridium difficile infection. J Pharm Pract. 2013;26(5):464–475. doi:10.1177/0897190013499521

  3. Park T, Cave D, Marshall C. Microscopic colitis: a review of etiology, treatment and refractory disease. World J Gastroenterol. 2015;21:8804–8810. doi:10.3748/wjg.v21.i29.8804

  4. Madisch A, Hellmig S, Schreiber S, Bethke B, Stolte M, Miehlke S. Allelic variation of the matrix metalloproteinase-9 gene is associated with collagenous colitis. Inflamm Bowel Dis. 2011;17:2295-2298. doi:10.1002/ibd.21640

  5. Iacobellis F, Narese D, Berritto D, et al. Large bowel ischemia/infarction: how to recognize it and make differential diagnosis? A review. Diagnostics (Basel). 2021;11:998. doi:10.3390/diagnostics11060998

  6. Washington C, Carmichael JC. Management of ischemic colitis. Clin Colon Rectal Surg. 2012;25:228-235. doi:10.1055/s-0032-1329534

  7. Molnár K, Pintér P, Győrffy H, et al. Characteristics of allergic colitis in breast-fed infants in the absence of cow’s milk allergy. World J Gastroenterol. 2013;19:3824-3830. doi:10.3748/wjg.v19.i24.3824

  8. McGovern DP, Kugathasan S, Cho JH. Genetics of inflammatory bowel diseases. Gastroenterol. 2015;149:1163-1176.e2. doi:10.1053/j.gastro.2015.08.001

  9. Sasson AN, Ananthakrishnan AN, Raman M. Diet in treatment of inflammatory bowel diseases. Clin Gastroenterol Hepatol. 2021;19:425-435.e3. doi:10.1016/j.cgh.2019.11.054

  10. Narula N, Wong ECL, Dehghan M, et al. Association of ultra-processed food intake with risk of inflammatory bowel disease: prospective cohort study. BMJ. 2021;374:n1554. doi:10.1136/bmj.n1554

By Amber J. Tresca
Amber J. Tresca is a freelance writer and speaker who covers digestive conditions, including IBD. She was diagnosed with ulcerative colitis at age 16.